The injury the vasculature sustains due to reperfusion after a period of ischemia is a major cause of morbidity and mortality. This condition known as ischemia-reperfusion injury (IRI) often occurs as a consequence of infarction, shock, or organ transplantation. The effects of IRI can be localized, most often in the heart, lungs, intestines, or kidneys;or manifest as systemic effects in the form of multiple organ dysfunction syndrome (MODS). Compromised vascular barrier function resulting in damage to underlying tissues is common to all presentations of IRI. Reactive oxygen species (ROS) have been implicated as an important component of reperfusion injury. Although ROS can act as direct mediators of injury, ROS are also being recognized as important components of cellular signaling pathways. In endothelial cells, the small GTPase RhoA plays a key role in the regulation of vascular permeability through modulation of the actin cytoskeleton and cell-cell junctions. RhoA has been shown to contain a redox- reactive motif through which oxidation of two critical cysteine residues can regulate GTPase activity. Preliminary results indicate that RhoA is directly regulated by ROS in pulmonary microvascular endothelial cells. I hypothesize that ROS signaling in endothelial cells can directly regulate the activity of RhoA, resulting in increased vascular permeability and injury during ischemia-reperfusion. To elucidate the role of redox-regulation of RhoA in the pathogenesis of IRI, this project has three specific aims: (1) to investigate redox-mediated regulation of RhoA activity in endothelial cells, (2) to determine if redox-regulation of RhoA regulates vascular permeability in vitro, (3) utilize a mouse model of pulmonary ischemia-reperfusion injury to investigate the role of RhoA and ROS during IRI in vivo. The results of this project will provide insight into novel redox mediated pathways for controlling cytoskeleton dynamics and the role of RhoA in the regulation of vascular permeability. PUBLIC HEALTH RELEVANCE: Ischemia-reperfusion injury (IRI) is a significant cause of morbidity and mortality, often occurring as a consequence of infarction, shock, or organ transplantation. The biological mechanisms responsible for vascular injury during IRI are largely unknown. The results of this project will provide insight into novel cell signaling pathways which may be involved in the pathogenesis of IRI.